Health Gaurentee:
I would be ok with a week or two. Gives you time to examine the animal closely for signs of things like R.I and mites.
Genetic Gaurentee:
That's more for things you are paying extra for. If you get a straight up visual pied female, no cert needed. She's pied and you can see that. Now if someone sells you a female pyro pied (fire) that not super bright or say a low expression leopard pied, I would expect that the breeder would Gaurentee those genetics in writing. A good breeder has no problem putting in writing the equivalent of "these are the genes in the animal I just sold you....and I Gaurentee that". Again, often at expos breeders might not have certs for the animals brought. You should get a sales receipt for sure, I woukd make sure he writes down exactly what you are buying. Also ask if he can send you a PDF cert via email incase you sell it before you breed / prove it.
Gender ..... Just pop it:
Popping is reeeeeally easy. If they tell you they can't, ask them how they verify gender. The other typical way is probing. He should be able to show you something. Now if your paying for a girl (more expensive) and they do a bad job at popping the snake (don't press and roll at all) or flat out refuse to show anything and sell you a male then you paid a little extra for nothing. If your paint for a male, and you get a girl then that's a bonus in my books. (Unless you really needed the male for breeding)
Chris